￭ Protecting the system against thermal overload
The brake chopper protects itself and the resistor cables against thermal overload when
the cables are dimensioned according to the nominal current of the drive. The drive
control program includes a resistor and resistor cable thermal protection function which
can be tuned by the user. See the firmware manual.
Frames R1 to R4
Equipping the drive with a main contactor is highly recommended for safety reasons.
Wire the contactor so that it opens in case the resistor overheats. This is essential for
safety since the drive will not otherwise be able to interrupt the main supply if the chopper
remains conductive in a fault situation. An example wiring diagram is shown below. ABB
resistors are equipped with a thermal switch (1) inside the resistor assembly as standard.
The switch indicates overtemperature and overload.
ABB recommends that you also wire the thermal switch to a digital input of the drive
L1 L2 L3
1
2
3
4
5
6
13
14
3
4
1
2
K1
Θ
OFF
ON
L1 L2 L3
1
+24VD x
DIx x
ACS880
ACS880
Frames R5 to R9
A main contactor is not required for protecting against resistor overheating when the
resistor is dimensioned according to the instructions and the internal brake chopper is
in use. The drive will disable power flow through the input bridge if the chopper remains
conductive in a fault situation but the charging resistor may fail.
266 Resistor braking
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